Smart antenna technology is directed to antennas having the ability to change radio beam transmission and reception patterns to suit the environment within which radio communication systems operate. Smart antennas have the advantage of providing relatively high radio link gain without adding excessive cost or system complexity.
Smart antenna technology has been used in wireless communication systems for decades, and has recently been investigated for use in wireless local area networks (WLANs). In a WLAN, a client station (CS) is a device used by a mobile end user for communication with other stations within the same WLAN or with other entities outside of the WLAN. Central hubs that provide distribution services in WLANs are referred to as access points (APs). Access points are similar to base stations in wireless telecommunication systems.
A client station can be equipped with a smart antenna as well as an antenna steering algorithm that enables the antenna to switch electronically to a particular directional antenna beam. This enables the client station to communicate with its access point while achieving high performance.
Signal quality information, such as a received signal strength indicator (RSSI) or a signal-to-noise ratio (SNR), is typically used to determine or steer a preferred directional antenna beam. However, it is difficult to accurately measure signal quality information when the received signal includes undistorted signals plus random noise. In addition, the received signal itself may be distorted and directional interference may be added in the received signal. Consequently, signal quality information alone may not always be a reliable indicator of the quality of the radio link. This is especially true in radio environments that are rich with interference coming from other client stations and access points, or other types of noise and interference sources.
Once a directional antenna beam has been selected for a smart antenna, the quality of the radio link may change if the client station moves or an object moves into the radio link path. As a result, the selected directional antenna beam may no longer be the preferred antenna beam. To maintain communications, the other available antenna beams may be re-scanned for selecting a new preferred antenna beam. As noted above, the signal quality information alone may not always be a reliable indicator of the quality of the radio link when re-scanning.